1. Field of the Invention
The present invention relates to an on-demand type ink jet printing head with a plurality of ink nozzles formed in a planar configuration.
2. Description of the Related Art
A conventional on-demand ink jet printing head executes printing by jetting ink from hyper-fine nozzle holes onto a recording medium such as paper. A conventional on-demand ink jet printing head is illustrated in FIG. 3. An on-demand printing head typically comprises a cavity plate 1 formed on stainless steel or glass. Cavity plate 1 is formed with ink nozzle holes 2, ink passageways 3, ink pressurizing chambers 4 and an ink supplying path 5 by etching or other manufacturing techniques. A cover plate 6, e.g., an oscillatory plate, is superimposed on cavity plate 1. An ink flow path is formed by bonding or fusing the cavity plate and the cover plate together. Piezoelectric elements 7, each functioning as an electromechanical transducer element, are bonded to the external portions of the cover plate which correspond to ink pressurizing chamber 4. An ink supplying hole 8 is perforated in a portion of the cover plate. Electrodes (not illustrated) are provided on the upper and lower surfaces of piezoelectric elements 7. Upon application of voltage to the electrodes, distortion occurs in each individual piezoelectric element 7, thereby deforming the cover plate. As a result, the capacity of each ink pressurizing chamber 4 is reduced, and ink is jetted from ink nozzle holes 2. Printing is thus performed.
An on-demand type ink jet printing head such as that shown in FIG. 3 is simple in structure, is therefore small in size and inexpensive to manufacture. In addition, the ink jet printing head of the type shown in FIG. 3 is relatively silent. In the above-described printing head, however, it is difficult to dispose a plurality of ink nozzles in a planar configuration because of the contraints of head construction and nozzle manufacturing techniques.
FIG. 4 is a perspective view schematically illustrating one example of a printing apparatus comprising an on-demand type ink jet printing head. Such an arrangement utilizes a number of nozzles typically twelve, and up to a maximum of twenty four. A recording medium paper 9 is guided in the direction indicated by an arrow A. A platen 10 is positioned behind paper 9 for guiding the paper. Platen 10 also serves as a carrier roller that is rotationally driven by a driving source (not shown) with the aid of a shaft 11. A guide shaft 12 and a guide rail 13 are disposed in parallel in front of the platen 10. A carriage 14 is supported and guided on the guide rail 13. Carriage 14 reciprocates in the directions indicated by arrows B. Carriage 14 is loaded with the ink jet printing head depicted in FIG. 3. Ink is jetted onto recording medium 9 while driving the printing head in synchronization with the movement of carriage 14 to execute printing.
In the above-mentioned system, the rate at which the carriage moves must increase remarkably to speed up the printing process. If the carriage is accelerated, however, the points at which the ink hits the paper deviate, due to the slowness of the lateral movement of the paper. Alternatively, no ink may jet out because air is sucked into the printing head at an increasing rate with increasing carriage speed. Hence, any attempt to speed up printing encounters limitations. Typically a printing head is equipped with 12 or 24 nozzles, and hence its resolution is 8-dot/mm at a maximum. Consequently, high quality printing cannot be achieved.
It is an object of the present invention to provide an on-demand type ink jet printing head capable of performing high quality printing at a high printing device carriage speed.